View Full Version : AR15 Build/Interchangeability Questions

Shane Tuttle
July 31, 2012, 06:06 PM
I was looking on Palmetto State Armory and Brownell's websites to try and "build" my own. While I'm in the process of buying some books and such, I'm running into more questions than answers. As soon as I think I'll buy a lower or upper kit, there seems to be just too many parts I might replace that's in the kits. But as I try to find individual parts, I'm at a loss to know if they'll work.

For instance; This stripped upper:


It also has an "M4 feed ramp cuts" and "M4 profile barrel". Does this mean nothing with an A2 setup will work?

Going on Brownell's AR15build.com section I ran into obstacles such as these:

What's the difference between a standard buffer and a heavy counterweight buffer? Advantages/disadvantages?

How do you know if you need a small pin or large pin triggers? Is one better than the other?

This AR is planned to be built for range plinking but primarily for HD.

July 31, 2012, 07:01 PM
1. The complete M4-style upper will work with a complete A2 (traditional fixed stock) lower.

2. The AR design balances the gas port pressure against the sprung mass of the bolt carrier/buffer group. Heavy buffers are used to slow the extraction cycle. This comes in handy if your upper's gas port is too big or your ammo uses a slow powder or if you want a softer cycling rifle. Buffer weights are standard/unmarked, H1 (one tungsten weight), H2 (two tungsten weights), H3 three tungsten weights). I've never seen an A2 upper that needed a heavy buffer. I run H1 buffers in my 16" carbines to soften the cycle.

3. During the Clinton ban era, Colt had the stupid idea of making hammer/trigger groups with proprietary (big) pin sizes. This was because leftists imagined every AR could be converted to full auto baby killers by swapping M-16 fire control components (which use standard/small pins). Hint: big pin hammer/triggers require big pin lower and upper receivers, which were only available from Colt. Everybody else uses standard/small pin hammers/trigger groups.

July 31, 2012, 07:20 PM
1) M4 cuts in the receiver are only compatibility issues with the barrel (particularly the barrel extension, but those are not bought as separate parts... they're always affixed to the barrel). The short version is that the feed ramps were extended from the barrel extension to the receiver, lengthening them for better feeding. You can use an M4 ramped barrel with an unramped receiver, but one should never use a M4 ramped receiver with a standard ramped barrel. You'll end up with little gaps that catch bullet noses.

There are indeed A2 uppers and full length rifle barrels with M4 feed ramps... I built up an upper like that.

2) The heavier the buffer, the more resistance they provide, slowing the cycling. Some recommend that one uses the heaviest buffer that will still cycle the thing properly, but in practice, unless the thing is just beating itself up a standard or H buffer is just fine. This is irrelevant if you use an A1 or A2 fixed stock- those use a rifle buffer, not a carbine buffer.

3) DnPRK nailed it- if you don't have a Colt receiver, you have a small pin lower. If you would have a Colt receiver, you'd have to check.

Crow Hunter
August 1, 2012, 07:03 AM
Any Colt serial number from around LEO59000 and later has the smaller .155 pins including the Colt Manufacturing lines. Prior to that they are mixed productions.

Earlier than LEO50000 they are pretty much all the .170 pins.

Your best bet is probably to buy a stripped lower with your favorite roll mark, assemble it, then just buy a complete upper assembly set up the way you like it. Unless you are planning on doing quite a few, the tools that you should buy to make it easier will usually cost more than what you will save building just one rifle. (Now if you are doing it for fun, that is a different;))

August 1, 2012, 08:50 AM
it would prolly be easier to instead of buying a upper kit to buy everything seperatly? like the titanium firing pin an stuff like that?

Shane Tuttle
August 1, 2012, 09:30 AM
Thanks for the replies. It makes things clearer, now.

I'm almost sure I want a Spikes lower stripped receiver then assemble from there.

Ballpark guess how much I should expect to budget for tools if I want to build from scratch? I'm sure I'll be building more in the future and this is something I'd like to do just because.

August 1, 2012, 09:40 AM
it depends on the price like the JP Enterprises Enhancedbolt that is good for 60k rounds from brownells is $139 an paired up with a Failzero that is good for 50k rounds without lubrication an the carrier is $174. the carrier comes with gas key installed an staked. then add the titanium firing pin an that is $44.99 but with that setup you can be sure if something fails it won't be the firing group.

August 1, 2012, 09:59 AM

I would go with a Free Float hand Guard. I have started off a 300 Blackout Carbine Build. I chose a YHM Light Weight hand guard.

pretty decent video. If you have a good punch set you are already ahead of the game.

August 1, 2012, 10:41 AM
...I'm almost sure I want a Spikes lower stripped receiver then assemble from there.

Ballpark guess how much I should expect to budget for tools if I want to build from scratch? I'm sure I'll be building more in the future and this is something I'd like to do just because.

Do you plan to assemble the upper receiver too, Shane? If not, then you can get by with standard tools to build up a stripped lower. (Spikes is a great choice, BTW.) Maybe a punch or two, that's all you'd need. I've built up five stripped lowers and haven't bought specialized tools. (Well I did get a castle nut wrench for about $10.)

As far as the upper, you would need maybe $50-100 in tools to assemble but you can get almost anything you want factory built and test fired so I'd recommend going that route for just one upper. For more, then maybe the tools start to make sense. After your research and selection of the upper, just buy a quality brand and it's very hard to beat BCM or PSA or Spikes. I would not waste money on enhanced or nickel boron coated BCGs, a standard M16 style milspec BCG really can't be beat.

August 1, 2012, 12:22 PM
It doesn't take as many tools as one would think to build ARs. You can build a lower with just a couple roll pin punches and a 8oz hammer. It does help to have roll pin starter punches and a vise block, but you can get by with out. To build a upper you have to have a vise block and armorers wrench for the barrel nut.

August 3, 2012, 02:25 AM
Good luck on the build. Spikes is definitely a good brand to go with. Luckily they are local to me; I have built 2 lowers from them and they are excellent quality.

For tools I would recommend a good punch set, a vice block, AR wrench, and a rubber mallet.